PROJECT SUMMARY/ABSTRACT Preterm birth is the leading cause of infant mortality during the first four weeks of life world-wide. The overarching goal of this research is to enhance our understanding of the genetic and epigenetic mechanisms that mediate myometrial quiescence and contractility during pregnancy and labor, and their dysregulation leading to preterm birth. We suggest that progesterone (P4)/progesterone receptor (PR) maintains myometrial quiescence throughout most of pregnancy by inhibiting expression of inflammatory (e.g. IL-1b, IL-8, COX-2) and contractile (CAP) (e.g. OXTR, CX43) genes. We propose that this occurs via two basic mechanisms: (1) PR may tether to transcription factors (e.g. NF-kB, AP-1) bound to promoters of inflammatory genes and recruit corepressors to inhibit gene expression; (2) PR also may bind directly to promoters of genes encoding transcriptional repressors (e.g. ZEB1) to activate their expression. ZEB1, in turn, binds to promoters of CAP genes and recruits a repressive complex to inhibit their expression. By contrast, during the initiation of term and preterm labor, PR function in myometrium is impaired by its direct interaction with NF-kB, by increased expression of enzymes that metabolize P4 to inactive products, by decreased expression of PR coactivators and by upregulation of truncated PR isoforms (e.g. PR-A). The truncated PR isoforms may have reduced transcriptional and transrepressive activity. We postulate that these changes in inflammatory and CAP gene expression are mediated by alterations in chromatin modifications and structure. The goals of this proposal are to define the genes and mechanisms that underlie the inhibitory actions of P4/PR and differential actions of PR- A and PR-B on inflammatory and CAP gene expression, and to characterize the chromatin modifications that mediate myometrial quiescence and accompany enhanced CAP and inflammatory gene expression leading to term and preterm labor. To achieve these goals, we will use mouse models and human myometrial cells and tissues to: (1) define and characterize components of the complex of transcription factors/coregulators that interact with PR in the pregnant myometrium to mediate its anti-inflammatory actions and that interact with ZEB1 to inhibit CAP gene expression; (2) analyze expression and promoter-binding of these PR-interacting factors during pregnancy and with term and preterm labor and the effects of hormones and microRNAs in their regulation; (3) use RNA-seq and ChIP-seq to discover myometrial genes that are critical for the maintenance of pregnancy and initiation of labor and the underlying transcriptional mechanisms for their regulation. RNA-seq will enable discovery of genes involved in maintenance of pregnancy and the initiation of labor. The combined use of ChIP-seq will provide global insight into the transcriptional and epigenetic mechanisms that underlie these gene expression changes. Studies using PR-B-KO mice will elucidate the differential roles of PR-A vs. PR-B in regulation of the myometrial transcriptome. Collectively, our findings will reveal novel genes and pathways that can serve as therapeutic targets to prevent preterm birth and its consequences.